This invention relates to an electrophotographic color process for producing an electrostatic latent image, and more particularly to an electrophotographic color process which can produce a color copy that is excellent in the reproduction of an image of the human skin part of the original color photograph.
With respect to the process of producing an image of objects by electrophotography, the Carlson Method is well known and comprises the charging step in which a surface of a photoconductive plate is charged uniformly, the exposure step in which the electrostatic latent image of an original is produced by exposing a photoimage of the original on the surface of the photosensitive plate, the development step in which the electrostatic latent image is developed by toner, the transfer step in which the toner image developed is transferred onto the transfer paper, and the fixing step in which the toner image transferred on the transfer paper is fixed. However, the copy produced in this way is not satisfactory in the granularity and the tone reproduction characteristics.
In Japanese patent publication No. 14526/1975, a process has been disclosed wherein the photosensitive plate comprising the conductive substrate and the photoconductive layer is charged and the electrostatic latent image is produced by the image exposure and then uniform exposure of about 2-20 Lux. sec is executed on the whole surface of the photoconductive layer. As this method can eliminate the edge effect, the image of objects produced can improve in the tone reproduction characteristics, however, its granularity becomes worse.
On the other hand, with regard to three-color separation color electrophotography, the electrostatic latent image of each color separation image is developed by the first, the second and the third developing apparatus which are arranged in such a way as to correspond to each of the three-color separation images, respectively. The light decay curves of the surface potential, in the position of each developing apparatus, of the electrostatic latent images of color separation images produced on the photosensitive plate are different with each electrostatic latent image as shown in FIG. 1. The curve means that the relation among the surface potential V.sub.L1 of the first electrostatic latent image, the surface potential V.sub.L2 of the second electostatic latent image, and the surface potential V.sub.L3 of the third electrostatic latent image is represented as V.sub.L1 &gt;V.sub.L2 &gt;V.sub.L3.
When the first to the third electrostatic latent images are produced on the condition that the secondary charge volume and the uniform exposure volume are constant, the obvious improvement of the the color image produced by the first electrostatic static latent image can not be recognized in granularity and color tone reproduction characteristics. The color image produced after the development of the third electrostatic latent image is good in granularity and the color tone reproduction characteristics, but not good in the detail reproduction. As shown in FIG. 2, with respect to the developing agents corresponding respectively to the electrostatic latent images, the developing property is different in magenta toner, cyan toner and yellow toner, so the color copy produced is not good in color balance.